1. Field of the Invention
The present invention relates to a receiving apparatus, a receiving method, a program, and a receiving system. More particularly, the invention relates to a receiving apparatus, a receiving method, a program, and a receiving system for enabling a receiver receiving a code sequence coded in LDPC and punctured at least partially to provide faster convergence for the LDPC decoding of the code sequence.
2. Description of the Related Art
Communication systems use coding to conduct reliable communications over noise-plagued communication channels. Illustratively, wireless systems such as satellite networks are exposed to numerous noise sources stemming from geographic and environmental factors. For the communication channels of these systems, a theoretical upper limit known as the Shannon limit is stipulated as a fixed capacity representing the number of bits per symbol for a given signal-to-noise ratio (SNR). As a result, one desire of coding design is to attain a rate approaching the Shannon limit. This desire has a particularly close relation with bandwidth-limited satellite systems.
In recent years, techniques known as turbo coding have been developed as coding methods for achieving performance close to the Shannon limit. The techniques thus developed illustratively include PCCC (Parallel Concatenated Convolutional Codes) and SCCC (Serially Concatenated Convolutional Codes). Apart from the turbo coding techniques, another coding method known for many years as Low Density Parity Check codes (called LDPC coding hereunder) is again attracting attention.
LDPC coding was first proposed by R. G. Gallager in “Low Density Parity Check Codes,” Cambridge, Mass.; M.I.T. Press, 1963 (called the Non-Patent Document 1 hereunder). Recently, LDPC coding was again taken up by D. J. C. MacKay in “Good error correcting codes based on very parse matrices,” submitted to IEEE Trans. Inf. Theory, IT-45, pp. 399-431, 1999 (called the Non-Patent Document 2 hereunder), and by M. G. Luby, M. Mitzenmacher, M. A. Shokrollahi, and D. A. Spielman in “Analysis of low density codes and improved designs using irregular graphs,” in Proceedings of ACM Symposium on Theory of Computing, pp. 249-258, 1998 (called the Non-Patent Document 3 hereunder).
Recent studies have revealed that, as with turbo coding, LDPC coding provides performance closer to the Shannon limit the longer the code length involved. Noted for its property of letting minimum distance remain proportional to code length, LDPC coding offers such advantages as an improved block error rate and the virtual absence of the so-called error floor phenomenon that has been observed as characteristic of the decoding in turbo coding arrangements.
The above-mentioned advantages set the stage for LDPC coding to be adopted definitively by DVB (Digital Video Broadcasting)-T.2 (see “DVB BlueBook A122 Rev. 1, Frame structure channel coding and modulation for a second generation digital terrestrial television broadcasting system (DVB-T2)” at the DVB website updated on Sep. 1, 2008 (accessed on Mar. 17, 2009 on the Internet <URL: http://www.dvb.org/technology/standards/>; called the Non-Patent Document 4 hereunder). DVB-T.2 is the next-generation terrestrial digital broadcasting standard currently prepared (March 2009) by ETSI (European Telecommunication Standard Institute).